One example of an apparatus that can realize the retrieval of desired information programs based on the program number (PNO) is illustrated in FIG. 6. In this figure, a mechanism block 1 contains a magnetic tape 2 having program numbers corresponding to a plurality of information programs. The magnetic tape is wound on supply reel 7 and take-up reel 8. The tape runs along the circumferential surface of a rotary drum 3, within a section having an angular range of 90.degree.. The tape loads a pair of heads 4a, 4b arranged with an angular interval of 180.degree.. capstan 5 and pinch roller 6 operate to drive the magnetic tape 2 in a conventional manner. For example, when the magnetic tape 2 is run at an ordinary speed for reproduction or even at an intermediate speed (about 10 times or more than the ordinary speed). the driving force of he capstan 5 and pinch roller 6 is adequate. However, when the tape is run at a high speed (about 100 times to 200 times the ordinary speed for reproduction) it is driven by the supply reel 7 or take-up reel 8.
A reproduction amplifier 9 is connected to the block 1 and amplifies reproduced signals alternately picked up from the heads 4a, 4b. A program number reproducing circuit 10 receives the amplified signals and operates to reproduce program numbers, as subcode information, from the heads 4a, 4b sent via reproduction amplifier 9. A current program number holding circuit 11 holds program numbers of the current position reproduced by the program number reproducing circuit 10.
An operation part 12 sends to a control circuit 15 and an object PNO holding circuit 13 a program number input identifying a desired search position. Control circuit 15 produces an initiation instruction input for controlling the reproducing operation of the information program and the search operation. Object program number holding circuit 13 operates to hold program numbers identified as a search position input by the operation part 12. Program number comparison circuit 14 acts to compare values of the program numbers held in the current program number holding circuit 11 and object program number holding circuit 13. Control circuit 15 controls a mechanism drive circuit 16 based on an output sent from the operation part 12 and program number comparison circuit 14. Circuit 15 also controls the mechanism block 1 in an operation mode, such as a reproduction mode, and in a search mode, such as a search operation for information programs.
The operation of an apparatus having the structure of FIG. 6 may be easily explained. Let it be assumed that a program number of the desired search position is designated by the operation part 12. A program number reproduced by the program number reproducing circuit 10 is held in the current program number holding circuit 11. Let it also be assumed that the program number of the search position is held in the object program number holding circuit 13.
When initiation of a search operation is designated by the operation part 12, the control circuit 15 Will shift the mechanism drive circuit 16 to the high speed search operation mode in the FWD or REV direction based on the output from the program number comparison circuit 14, namely the result of a comparison of values of the current program number and object program number. In this manner, the mechanism drive circuit 16 controllably drives the mechanism block 1.
During the high speed search operation, the control circuit 15 always Watches the output of the program number comparison circuit 14. When the program numbers in the current program number holding circuit 11 and the object program number holding circuit 13 match, the control circuit 15 controls the mechanism drive circuit 16 to set the mechanism block 1 to an intermediate speed running condition. In this manner the apparatus initiates a so-called "precise quick-start of reproduction".
When the object program number is detected during preparation for a precise quick-start of reproduction, the search operation at the desired search position is completed. However, if the starting end or terminating end of the magnetic tape is detected by a detection means (not illustrated) during the high speed search operation, the high speed search operation is interrupted.
In one approach, while the magnetic tape 2 is caused to run at a high speed in a high speed search operation, the program numbers recorded on the magnetic tape 2 are reproduced by the program number reproducing circuit 10 and, simultaneously, the search position in which the object program number is recorded is retrieved. However, in the case of the R-DAT format identified above, the program numbers are recorded only in the 300 frames (9 seconds at the speed of ordinary reproducing operation) at the heading section of individual information programs. Therefore when the magnetic tape is caused to run at 200 times the speed of the ordinary reproducing operation, for example, during the high speed search operation, the head passes the part recording the program numbers only during a period of 45 msec.
To solve this problem for the R-DAT format, a so-called relative speed servo technique is employed for realizing the high speed search operation. In particular, the number of rotations of rotary drum 3 is changed in accordance with the running speed of magnetic tape 2. Thus, the relative speed of recorded patterns with respect to the head during the high speed search operation in the R-DAT is fixed. Specifically, during the high speed search operation, the drum rotates at about 200 times its speed in the ordinary reproducing operation. The high rotational speed is used primarily in the REV direction. However, the signal reproduced from the magnetic tape includes a variety of distortions and does not appear in an ideal condition. Therefore, the magnetic tape running speed in the actual high speed search operation has been set to a speed slightly lower than 200 times that of the ordinary reproduction speed. The lower speed is designed to provide a margin for always realizing a stable high speed search operation.
As explained previously it is necessary in the above-described approach to always read the program numbers recorded on the magnetic tape during the high speed search operation. It also is necessary for the running speed of magnetic tape to be set to a speed significantly lower than the upper limit defined by mechanism limitations (for instance, the speed at which the magnetic tape runs stably and is not subject to damage). This speed occurs, for example, at only 150 times the ordinary reproducing speed in order to always read, under a stabilized condition, the subcode information such as program numbers on the magnetic tape.
Because of these competing considerations, the high speed retrieval technique used in the current R-DAT system may not provide sufficient high speed retrieval performance. Moreover, it also has been difficult to exceed the upper limit of the retrieval speed, due to the format used in R-DAT.